Deer mice are known for being quite promiscuous. In fact, it is not uncommon to find a litter of deer mice with multiple fathers. Dr. Hopi Hoekstra and colleagues at Harvard University's Department of Organismic and Evolutionary Biology discovered that the tail of deer mice sperm have longer midsections than found in monogamous mice. What this means is that their sperm can swim better and faster, thereby reaching an egg sooner than sperm from other prospective fathers. The research team identified the gene responsible for producing the olympic-sperm, PrKar1a. The findings from this study may also help improve human fertility since other research suggests this same gene might be involved in human fertility.
Fisher HS, Jacobs-Palmer E, Lassance J-M, Hoekstra HE. The genetic basis and fitness consequences of sperm midpiece size in deer mice. [pre-print from BioRxiv]